Agricultural combines typically include a cleaning system below and rearward of the threshing unit. The cleaning system includes a cleaning fan oriented horizontally and transversely across the combine to create airflow through one or more sieves.
Crop material is deposited on the sieves for pneumatic and mechanical separation. The amount of air required for pneumatic separation depends on many factors, such as grain type, grain test weight, and grain throughput. The rotational speed of a combine cleaning fan is typically variable to allow changing air velocities as required to clean the various seed sizes and weights harvested by a combine. In addition, when more crop is present, it is typically desirable to increase the cleaning fan rotational speed, and when less crop is present, it is desirable to decrease cleaning fan rotational speed.
Combine cleaning fans are either hydraulically driven or belt driven. With a hydraulic drive, electric current to a solenoid valve is controlled to vary the oil flow to the hydraulic motor. With a belt drive, an electric motor varies the pitch diameter of the driver sheave to control the cleaning fan. When a controller controls the current to either the solenoid valve or electric motor, the cleaning fan speed can be sped up when high throughputs are entering the combine and slowed down when lower throughputs are entering the combine.
The combine's crop throughput will typically change within a given field or swath of field due to a variety of causes, for instance, changes in terrain, differing plant populations, or simply exiting and entering the crop row at the ends of the field. It would therefore be desirable to vary the rotational fan speed in real time in response to the varying conditions, such as crop density and the like. Many systems presently in use do not vary cleaning fan rotational speed in real time. The speed is set at the start based on an estimate of the crop throughput, and the speed is adjusted when detected grain loss is outside the tolerable limits.
Known control systems that can vary the rotational speed of the cleaning fan responsive to changing conditions, such as disclosed in Hoskinson et al., U.S. Pat. No. 6,591,145, adjust the cleaning fan speed based on outputs of grain loss sensors at the rear of the combine. This system monitors the grain ejected from the system, and at some pre-determined unacceptable grain loss level, adjusts the cleaning fan rotational speed. However, it must be emphasized that this system measures grain loss after it has already been lost by the combine. That is, this system requires a level of grain loss prior to making adjustments to cleaning fan speed because it only monitors the grain leaving the system. Rather than anticipating a situation in which grain may be lost, known control systems such as this only adjust cleaning fan speed after valuable crop has been lost.
It is desirable to adjust the cleaning fan speed based on the amount of crop entering the combine cleaning system rather than the crop already lost by the system. Thus, what is sought is a device that can sense the amount of crop material about to enter into the cleaning system and adjust the cleaning fan rotational speed to the amount of crop material moving through the system, which is simple and easy to operate and otherwise overcomes one or more of the shortcomings set forth above.